The present invention relates to proximity systems and, more particularly, to capacitance controlled oscillator circuits for sensing the proximity of animal tissue to a given location.
The prior art is replete with examples of proximity devices for sensing the presence of persons or material to provide an alarm or other indicating signal. The devices use a variety of circuits, including oscillator circuits, wherein the impedance of the oscillator is changed in response to proximity detection to initiate or terminate oscillation. By way of example, common oscillator and sensing circuits have been used in portable and permanent intrusion alarm systems to provide oscillations and detections of the oscillations upon the touch of a particular area so that an alarm is initiated or transmitted to a security station. In other instances, the sensing circuits are utilized to detect the presence or absence of liquid in a particular area by sensing the change in capacitance caused by the presence of the liquid and thereafter initiating indicator or alarm devices. Such devices have also been used in security systems to protect individual items wherein the capacitance change caused by the touch of that item by an individual will initiate oscillation and signaling of an alarm circuit.
In still other instances, the proximity detector oscillator circuits have been used to provide foul detection in bowling alleys. In such cases, the detector usually takes the form of a wire or plate which is coupled to sense the change in capacitance as the foot of a bowler passes over the foul line. The plate or wire is attached to the oscillator circuit to initiate oscillation when the foot or other part of the body passes the foul line and thereby initiate operation of an alarm signal. The most common devices include oscillator circuits formed by vacuum tubes or transistors controlling the application of current to a detection device which initiates the indicator or alarm signal when the current increases beyond a predetermined value.
While the above and similar devices have been successful in providing proximity indications, the same have generally suffered from shortcomings due to lack of sensitivity and influences by stray and unwanted capacitance changes. When used in situations where great sensitivity is required, the rate of false alarms is high and the accuracy with respect to actual proximity must be reduced to reduce the rate of false alarms. In instances where the detectors are used in bowling alleys and similar environments for foul detection, the systems have been somewhat complicated and cumbersome and require greater complexity than is practicable for inexpensive and reliable use. In addition, the prior art systems are incapable of being easily installed with the requisite sensitivity and accuracy.
Accordingly, the present invention has been developed to overcome the shortcomings of the above-known and similar techniques and to provide an oscillator proximity detector system with increased sensitivity and reliability.